In large part, details outlined in the above post remain consistent, though with some revisions to overall wind tendency. Therefore, provided here are the weather conditions expected for Wednesday, July 17th, for the greater Montreal area.

Temperature/Humidity

Limited by the substantial cloud cover described in the previous posting, a maximum temperature of 26-27 C is likely by mid-afternoon. Owing to continued cloud coverage into the evening period, however, temperatures would not drop significantly (24 C). Humidity would be high throughout the morning to afternoon before dropping to moderate for the late-evening. Thus, a maximum humidex of 31 C is favorable by mid-afternoon, and 28 C for the late-evening.

Precipitation

In response to a broad area of low pressure advancing from the South, extensive cloud cover will likely overspread this region for the day, in the form of mid- to high-altitude cloud cover. This would be joined by a progressively low-altitude stratiform cloud deck for the evening. While light rainfall will become increasingly possible near midnight (60% probability), the previous lack of solar heating would limit instability considerably. Therefore, thunderstorms are not expected within the bands of light to moderate rainfall at the Northern tier of the parent low pressure system. The periods of light rainfall themselves should narrowly occur after display time and become more persistent overnight.

Wind

Wind speeds remain light to occasionally calm throughout the day. As such, speeds should be 6-9 km/h for the day. Consistent with a slightly quicker Northward migration of the low pressure system, wind direction should be SSW for the day, including into the late-evening. This would allow the smoke to move gently clear to the right (at all altitudes) of the La Ronde audience. Periods of extensive smoke accumulation are favorable during more active segments, along low- to mid-altitude, and if/when smoke-rich products are used. The display would appear haziest towards La Ronde’s right.

If necessary, another update will follow by early this afternoon (July 17th) to address wind speed/direction, as well as if periods of rainfall are expected to advance sufficiently early enough to narrowly coincide with display time.

Trav.

For the seventh display day (July 21st), a mid- to upper-level area of low pressure will circulate over the region. Together with periods of solar heating and moderate humidity, this system would create instability suitable for convective showers and sparsely-distributed non-severe thunderstorms. Precipitation collectively would carry with it a 40% probability due to the scattered nature of the convection. By mid-evening, however, this convective rainfall would subside.

The cooler air mass associated with this system will resume the cooler than normal regime left behind by July 17th-July 18th for this region. As such, for the greater Montreal area, the maximum temperature should be 22-23 C, dropping to 19 C by late-evening under partly cloudy skies. With moderate humidity, this would create a maximum humidex of 26 C, and then 23 C for the late-evening.

Winds should largely be in the form of NNW to NW for the day, including for the evening period, at 9-12 km/h (breezier during the afternoon). This would cause smoke accumulations to move reasonably quickly clear to the left of the on-site audience. Thick accumulations are not favorable. Note that wind direction could transition to light WSW to SW in time for the late-evening and so will be carefully monitored/considered in the next report.

Another update will follow this late-evening (July 20th) into early-predawn July 21st.

Trav,

Forecast details presented in the above posting remain valid. Therefore, here are the expected weather conditions for Wednesday, July 21st for the greater Montreal area.

Temperature/Humidity

The aforementioned broad mid- to upper-level low will circulate over this region, most likely causing the coolest July 21st in 8 years. As such, a maximum temperature of 22-23 C is favorable, decreasing to 19 C by late-evening. Humidity would be borderline moderate-high for the afternoon, causing a maximum humidex of 27 C by mid-afternoon, and a value of 21 C for the late-evening.

Precipitation

Modest instability would be present during the afternoon. Some periods for solar heating, along with borderline moderate-high humidity, would yield scattered convective rainfall and isolated non-severe thunderstorms in this region as lift supplied by the mid-/upper-low increases. Partly cloudy skies (consisting of cumulus clusters) would be present for the afternoon-evening period, with a suppression of convection shortly after sunset.

Wind

Wind speeds are largely in the form of breezy Northerlies to NNE (14-18 km/h) for the day. By late-evening, wind direction does change to light WSW (4-7 km/h). This would allow smoke accumulations to drift gently towards central and right-hand sections of the La Ronde audience, although extensive smoke accumulation is not favorable. The display, however, would gradually appear hazy deeper into it.

Another update would follow by early this afternoon (July 21st) to address wind speed/direction, if necessary.

Trav.

Directional tendencies for this late-evening (July 21st) should be more in the form of light ENE (5-8 km/h), allowing the smoke to conversely move gently towards Notre-Dame Street, especially nearest to the bridge (and that section of the bridge itself). Smoke accumulations are still not expected to be thick, but the display would appear hazy from that vantage point.

EDIT: Owing the more amplified lift into the late-evening, sparsely-distributed convective rainfall/isolated non-severe thunderstorms will be possible through to the late-evening (collectively a 30% probability). This would be another revision.

Trav.

An area of low pressure will advance into E. Ontario to Southern Quebec for the final display day (July 24th). The warm front associated with this system would gradually lead to increasing cloudiness, in the form of cirrus, by the early-afternoon. By late-evening, a layer of mid-altitude cloud would overspread the regions in conjunction with the continuous coverage of cirrus. Convective rainfall associated with this warm front would not typically occur until the predawn of July 25th.

In response to this system, a strengthening SSE flow (speeds of 14-18 km/h by mid-afternoon) would develop over these regions, allowing for very warm conditions, as well as borderline moderate-high humidity. As such, a maximum temperature of 27 C is favorable for the greater Montreal area by mid-afternoon, along with a humidex of 31 C at that time. By late-evening, this declines to 22 C (humidex of 26 C). At the same, this would allow accumulated smoke from the fireworks would move reasonably quickly, at all altitudes, clear to the right of the La Ronde audience. Significant accumulations are not favored.

Another update will follow late this evening (July 23rd) into early-predawn tomorrow (July 24th).

Trav.

Consistent with the above posting, here are the expected weather conditions for the final display day of 2021 (Saturday, July 24th) for the greater Montreal area.

Temperature/Humidity

Ahead of the aforementioned warm front ejecting East will be an environment characterized by an enhanced circulation of warm, moist air and increased cloudiness. In light of this warming/moistening regime, a maximum temperature of 27 C is favorable. Borderline moderate-high humidity would yield a maximum humidex of 31 C. The late-evening temperature would be 22 C, and with steady humidity levels, a humidex of 26 C is likely.

Precipitation

As the warm front advances East, a continuous layer of high-altitude cloud (cirrus) will overspread the area throughout much of the afternoon, gradually in conjunction with a mid-altitude layer of cloud by late-evening. As such, mostly cloudy skies are favored for the evening, though convective rainfall associated with the warm front should hold until the predawn of July 25th.

Wind

Breezy SSE winds (14-17 km/h by mid-afternoon) should be dominant for the day, including into the evening period. This would allow smoke accumulations to drift sufficiently quickly clear to the right (at all altitudes) of the on-side audience. Extensive accumulations are unlikely.

Trav.

Thank you, Trav! I didn't realized that it could have been the closing show tonight... Well, it is the night of a first “prelude” 5-minute display, according to the announcement made this morning...

Fred

Hi Fred,

You’re very welcome!

From what I observed for each of these eight fireworks nights, despite the high frequency of thunderstorm risks this late-Spring to Summer, it seems likely that this edition of Montreal fireworks would have featured overall better than average weather conditions. Indeed, there was not a single situation when wind direction was too much of an issue, as it is likely that there was no fireworks night where the winds were displacing the smoke towards La Ronde directly. At the most, June 19th and July 14th would have likely featured smoke accumulations drifting towards right-hand and left-hand sections, respectively. However, there was never a night where the entire audience would be engulfed in a (thick) layer of smoke and, thus, observing falling debris. What was more unusual this year, however, was that the frequency of smoke moving towards sections of the bridge was high. To that end, 50% of the fireworks nights (June 19th, June 26th, July 3rd, and July 21st) would have likely induced situations that caused accumulations of smoke to reach the bridge.


Wind speeds were also generally good – like usual, many fireworks nights were under the influence of light winds, but there were no cases of extremes (i.e. neither overly light/calm nor overly strong). The strongest winds were present for the closing night (July 24th), but nothing that would have endangered the show. The greatest potential for thicker smoke accumulation would have likely been during the July 17th display, when humidity was high and wind speeds were light. That said, smoke accumulations, while thick, would have been greatest to La Ronde’s right, rather than over the audience. A similar situation was likely during the evening of July 10th.

While observed temperatures did not exhibit too much variability amongst display times, there was a more notable difference between the warmest and coldest nights. Indeed, July 14th had the warmest conditions (24-25 C) during display time, while July 3rd brought with it the coolest conditions (16-17 C). Humidity was highest during the July 14th and July 17th displays, with July 14th being the only display day to feature very high humidity, including during display time.

Finally, only one display day (June 26th) featured rainfall during a show. Approximately 70% of this display would have coincided with a persistent light rainfall. A near-miss situation also occurred on July 21st, when an isolated slow-moving thunderstorm was in the general area (but far to the West of the fireworks site), over West Laval into the West Island, during the late-afternoon/prior to sunset.

Trav.